Pavement in the form of city streets, county roads, airports, state and interstate highways, is one of the most critical elements of a nation's infrastructure. Managing the serviceability of this critical public resource involves obtaining an accurate measurement of the condition of the pavement and relating such conditions to other critical information such as traffic, climate and design information so that current and future needs can be determined and effective maintenance and reconstruction programs can be formulated.
Fundamental to an effective maintenance and reconstruction program is obtaining of very accurate information concerning the condition of the pavement. At the present such procedures for obtaining information are very time consuming and labor intensive and are inherently inaccurate and unreliable. Despite the expenditure of large amounts of sums, major reconstruction appropriations are often founded upon very inaccurate assessments of the pavement condition and the condition of the subgrade and foundation beneath the pavement.
Despite a number of attempts that have been made to develop equipment for testing the condition of the pavement, most public agencies have utilized a manual system of analyzing the condition of the pavement by the human eye by directly viewing the pavement surface or indirectly viewing the pavement through the use of photographs that have been taken of the pavement. In the later process, the photos are analyzed by the human eye to determine the presence and severity of pavement distress features. U.S. Pat. No. 3,151,235 granted Sept. 29, 1964 to Greenshields is an example.
In a somewhat similar context, mobile equipment has been devised in the past for determining the roughness of the road or pavement. Examples of such mobile equipment are illustrated in U.S. Pat. No. 3,983,746 granted to Ross A. Phillips et al. on Oct. 5, 1976 and U.S. Pat. No. 4,422,322 granted to Elson B. Spangler on Dec. 27, 1983.
More recently Highway Products International, Inc. of Paris, Ontario, Canada has developed a "automatic road analyzer" that has a van having a piezo resistant accelerometer mounted on the rear axle for measuring the longitudinal profile of a lane of pavement. It also has a front sensor bumper bar that is seven feet long with fold-up wing-type extensions that extend out to a full lane width of twelve feet. The sensor bar has ultrasonic transducers mounted on twelve inch centers across the bumper for measuring the transverse profile of the road as the van moves down the lane. Rather than taking photographs of the surface of the roadways, the Highway Products International, Inc. equipment also utilizes video cameras for continuously capturing an oblique view of the right-of-way pavement surface that may be visually inspected and kept for retrieval purposes. It should be noted that to cover a full twelve feet lane width the Highway Products International, Inc. equipment requires the implementation of special wide load traffic control procedures because the equipment extends outwardly to a width of twelve feet (wide load). It is very difficult to utilize such equipment during normal hours on a highway or to operate the equipment at the normal traffic speed such as fifty-five miles per hour.
Another company--Earth Technology Corporation, through its Pavement Condition Evaluation Services of Sparks, Nevada, is experimenting with placing three linear slit video scanning cameras either along the front bumper or along the back bumper of a van as the van moves over the pavement for scanning one pixel line at a time to develop information concerning the longitudinal and transverse profile of the pavement and to identify the presence and severity of surface distress features. Although Earth Technology Corporation hopes to be able to operate such a system at normal traffic speeds, at the present time it appears unable to do so.
It has been recognized for many, many years that the layered system reaction modulus and hence the condition of the subgrade and base may be evaluated by measuring the deflection of the pavement with respect to a known applied load in which the load may be stationary or mobile. Several attempts have been made to provide equipment for determining pavement deflection. One such device is shown in U.S. Pat. No. 4,406,823 granted to Jean-Claude Gressin on Oct. 18, 1983. An earlier effort along this line is shown in U.S. Pat. No. 27,875 granted to G. Swift on Jan. 8, 1974. U.S. Pat. No. 3,888,108 granted to Frank Brands on June 10, 1975 is concerned with measuring of an energy pulse through the pavement as an indicator of its structural strength.
Moreover, reinforced concrete and asphalt pavements absorb the sun's heat during the day and gives off thermal radiation at night. The pavement surface radiation pattern is closely related to the subsurface physical conditions, such as the type of soil, moisture distribution, or the like. Any variation in the subsurface conditions distort the heat emission pattern of the pavement surface. The heat pattern variation therefore can be related to changes taking place under the pavement in response to the variation in the weather conditions or the immediate environment surrounding a section of the pavement.
In order to conduct such a subsurface exploration of the pavement, the use of infra-red cameras are used to capture the pavement surface temperature profile at night from a surveillance vehicle. The pavement or field heat distortion patterns obtained by the infra-red cameras are interpreted by comparing them to a set of known and/or standard temperature profiles, either laboratory developed or measured, of a best-fit basis or analysis. The standard or known thermal patters are obtained from, for example, laboratory tests or experiments on laboratory-manufactured concrete, asphalt slabs, concrete slabs, or the like, supported on a variation of known soil layers having known moisture content distribution substantially representing field conditions.
An object of this invention is to provide pavement inspection equipment that includes a mobile vehicle such as a van that does not require the use of any special traffic procedures and that can be utilized at all hours of the day without disrupting or detouring or slowing normal traffic.
A still further object of this invention is to provide pavement inspection equipment that is capable of obtaining very reliable and accurate information concerning not only the longitudinal and transverse profile of the pavement, but identification and classification of pavement distress features such as cracks, potholes, slab displacements, and pavement separations.
A still further object of this invention is to provide a novel pavement inspection equipment which is also capable of efficiently carrying out pavement sub-surface inspection or exploration for information on types of base and/or sub-grade soils and moisture content distribution thereof.
A still further object of this invention is to provide unique pavement inspection equipment that is capable of obtaining very accurate information concerning the condition of the pavement at a very low per mile inspection cost that is in a summarized and usable form that can be readily utilized by those persons who are responsible for pavement maintenance and servicing.
These and other objects and advantages of this invention will become apparent upon reading the following detailed description of a preferred and alternate embodiments.